AD _

o EVALUATION OF REQUIREMENTS FORi MILITARIZATION OF 3-kW FREE-PISTON

STIRLING ENGINE GENERATOR SET

S Thomas J. MarusakMechanical Technology Incorporated968 Albany-Shaker RoadLatham, New York 11110

January 1982

Final Report

Approved for Public ReleaseDistribution Unllmlted

SPrepared for LECTE

_: S APR 1 9WC. U.S. ARMY MOBILITY EQUIPMENT RESEARCH 1419.~ AND DEVELOPMENT COMMAND

S Ft. Belvoir, Virginia 22060 Em

82 04 13 140

.................-. . .........................--"

Il

The views, opinions, and/or findingscontained in the report are those of theauthor and should not be construed asan official Department of the Armyposition, policy, or decision, unless

* so designated by other documentation.

SECURITY CLASSIFICATION OF TMIS PAGE ("on Dote Entre,.) ._..READ INSTRUCTIONSREPORT DOCUMENTATION PAGE BEFORE COMPLETING FORM

I. REPORT NUMBER 2. Q5VT ACCESSION NO. 3,'IENT'S CATALOG NUMBER

4. Ti'TLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVEREDEvaluation of Requirements for Militarization Final Reporto f 3 k W F r e e - P i s t o n S t i r l i n g E n g i n e G e n e r a t o r

_ ._ P E R F O R MI N G _ _ _ _ _R E P O R T _NU M B ESets s. PERF|O'RMING ORG. REPORT NUMUERSets_

82TR207. AUTHOR(") S. CONTRACT OR GRANT NUMBER(e)

Thomas J. Marusak DAAR70-81-C-0115

S. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASKMechanical Technology Inc. AREA & WORK UNIT NUMSERS968 Albany-Shaker RoadLatham, NY 12110

11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATEU.S. Army Mobility Equipment January 1982Research and Development Command IS. NUMBER OF PAGESFort Belvoir, Virginia 22060 210

IC4 MONITORING AGENCY NAME A ADDRESS(It different from Controlling Office) IS, SECURITY CLASS. (of this report)Same Unclassified

NIDa, EC LASSI FI CATION/DOW'NGRADINOSCHEDULE

1S. DISTRIBUTION STATEMENT (of thls Report)

Approved for Public Release; Distribution Unlimited

17. DISTRIBUTION STATEMENT (of the abstruct entered In Block 20, it dIffe.ent from RePort)

IS, SUPPLEMENTARY NOTES

19. KEY WORDS (Continue on reverse aide it necesesry and Identify by block number)

Free-Piston Stirling Engine Silent Tctical GeneratorLinear Alternator Parameter ComparisonMobile Electric Power

20. ABSTRACT (Contiu"o n reverse eside if ne*ce.r md Identify by block numbr)\The design evaluation study assessed the capability of the free-piston

Stirling engine (FPSE) to meet requirements for military mobile electricground power. Operational requirement parameters included physical,thermodynamic, audio, material, operational, and electrical. Test daja anddesign calculations indicated that, with continued development, the FPSE canmeet or exceed all of the military requirements for 3 kW silent tacticalgenerators operating on military logistic fuels.*

DD , OA N IS 1473 EDITION OF I NOV 65 IS OBSOLETE ISECURITY CLASSIFICATION OF THIS PAGE (iWun Date Enrred)

a- EXECUTIVE SUMMARY

Free-piston Stirling engines (FPSE) are advanced conversion power syytemsthat operate with two moving parts to produce electrical power from mostany fuel source, with high efficiency and high reliability. MechanicalTechnology Incorporated (MTI) is developing the FPSE for stationary com-mercial applications in the size range below 10 kW. Because of the poten-tial strategic and logistics advantages offered by these machines, theU.S. Army Mobility Equipment Development Command has contracted MTI toproject the capability of the FPSE to meet requirements for military groundpower. This report documents the results of that study.

The methodology employed in this study involves the comparison of test

data and design calculations with military requirements and standard. documents. Because the current development is oriented toward commercial

applications, engineering projections were made to evaluate the feasibilityof adapting the FPSE for military use.

Operational requirement parameters were divided into six categories:physical. thermodynamic, audio, material, operational, and electrical.The results of the ensuing parametric assessment are summarized in thetable that follows.

Meets orExceeds Below

Parameter Requirements Requirements Comments

Physical X Component TechnologyAdvancement Required

Thermodynamic X to Meet Weight Speci-ficat ions

Audio X

Materials X

Operational X

Electrical X

iii

a e--......*. ......-.:.aa ...... ot .. ..

Of the six categories assessed, only the physical requirement for low

system weight would demand additional technological development for FPSEst to have the capability for complying with military specifications. In

all othitr regards, the FPSE was found to have the capability for meeting

or exceeding the requirements. Further, when comparing the projectedmilitarized FPSE generator system with alternative geaqrators from theexisting standard family, the FPSE was determined to be potentially superiorin all aspects.

The specific conclusions that were drawn from the study are stated asfollows:

* The state of the art of FPSEs allows for currentcommercial hardware designs to achieve a significantportion or the military requirements and standards.

Engineering projections show that, in the near term,the FPSE can be developed to comply with allmilitary requirements for ground power.

e Present FPSE hardware designs compare most favorablywith alternative generator sets now in the standard

family.

Adv&nced FPSEs will surpass the operational

characteristics of alternative standard familygenerator sets ir All respects.

a The onerational and developmental testing of a FPSEgenerator operating with military logistic! fuelcapability could be established by 1984.

* A system development program needs to be implementedin order to adapt commercially oriented FPSF technology

for military application.

iv

- -

PREFACE

The work completed under this study was authorized by the U.S. Army MobilityEquipment Research and Development Command, Fort Belvoir, Virginia, undercontract number DAAK70-81-C-0115. This volume documents the entire programeffort associated with Task 1, Design Evaluation. A program plan was pre-pared and submitted separately in fulfillment of the requirements for Task 2,

x !Development Plan. This document comprises the Scientific and Technical Re-port as required by the Contract Data Requirements List DD Form 1423

lb (article A002).

The author gratefully acknowledges the enthusiastic support provided by theContracting' Officer's Technical Representative, Mr. Paul Arnold. Addi-tionally, the following technical contributors are listed for recognitionof their efforts in this project: Dr. R. Ackermann, Dr. Suresh Bhate,

1: .Mr. G. Dochat, Mr. R. Farrell, Mt. B. Goldwater, Mr. J. LaPointe, and

Mr. N. Vitale.

Accession ForNTIS GRA&IDTIC TAB Q3Unannounced [Justification

Di stribution/Availability Codes

Avail and/orDist Special . -pv

V

-7

TABLE OF CONTENTS

SECTION PAGE

EXECUTIVE SUMMARY ................ ................... ii

PREFACE ............. .......................... v

LIST OF FIGURES ........... .................... .

LIST OF TABLES .......... ..................... ... .. iii

1.0 INTRODUCTION .................. ...................... 1-11.1 Background ................. .................... 1-1

1.2 Technical Concept .............. ................. 1-1

1.3 Militarization Study ..... ............... . .. 1-5

2.0 METHODOLOGY ............. .................... ... 2-1

2.1 Test Data ............ ....................... 2-22,1.1 Technology Demonstrator Engine (TDE). . . . 2-22.1.2 "Prototype Engine" . ......... 2-10

2..1.3 Component Test Rigs ....... ............. 2-122.2 Design Data .......... ................... ... 2-12

2.2.1 The Engineering Model System ....... ... 2-162.3 Projected Design ........... ................... 2-20

3.0 PARAMETRIC COMPARISON WITH REQUIREMENTS ......... .. 3-13.1 Physical Parameters. . .................. ...... 3-3

3.1.1 Size ....... ......................... 3-3/I3.1.2 Weight . .... ......................... 3-7

3.1.3 Orientation . . ........................... 3-183.1.4 Mechanical .... ........ ........... 3-18

3.2 Thermodynamic Parameters ..... ............. . 3-23

3.2.1 Specific Fuel Consumption . . ...... 3-233.2.2 IR Signature ............ ........... 3-333.2.3 Exposed Metal Temperature . . . ...... 3-363.2.4 Multifuel Capability .............. ...... 3-36

3.2.5 Emissions ... ........... ........... 3-423.2.6 Fuel System Safety ....... ............ 3-45

vii

* PMFNWKWU PAGS-9I

* a......... ___________"___"______................_____ -

TABLE OF CONTENTS (Cont'd)

ASECTION PAGE

3.3 Audio Comparison . .. . ............... . 3-473.4 Materials Comparison. .. ....... . ........... . 3-513.5 Operational Power. .. .. ...... ........... . ... ...... 3-55

3.5.1 Power. .. ....... ............. . ...... .. 3-553.5.2 Frequency. .. ......... . .......... ........ 3-55 J

3.5.3 Climatic Conditions .. .. ...... ............ 3-583.5.4 Altitude Conditions .. .. ........ .......... 3-633.5.5 Reliability .. .. ...... ............. . ....... 3-643.5.6 Maintenance .. .. ...... ............. . ....... 3-683.5.7 Control .. .. ........ ........... . ........... 3-70

3.6 Electrical Parameters. .. .. ...... ............ 36-71

ik ~4.0 CONCLUSIONS . . . . . .. .. .. .. .. .. .. .. ... 4-14.1 Parameter Comparison Summary . . . . . . . .. .. .. 4-1

4.1.2 Summary of Theroyniami Parameters... . . . . . 4-5

4.1.3 Summary of Aurmdyno i Parameters. . . . . . . 4-5

4.1.4 Summary of Materialsi Parameters .. .. ......... 4-6 ~4.1.5 Summary of Operatl.onal Parameters .. .. ....... 4-6

4.1.6 Summary of Electrical Parameters .. .. ........ 4-74.2 Comparison with Alternative Military Generators .. . 4-74.3 Development Status .. .. ........ ........... . ....... 4-9

5.0 RECOMMENDATIONS. .. ......... . .......... ................ 5-15.1 Recommended Development of a Lightweight Linear

Alternator. .. ....... ............. ......... . ..... 5-1

5.3 Recommended Development Program for a MilitarizedFPSE Generator Advanced Development Prototype System 5-1

I ~ ~ xi -. ~ is viii -- I

41 ~TABLE OF CONTENTS (Cont')

SECTION PAGE

APPENDIX A REPLICATION OF REFERENCE DOCUMENTS .. ......... A-1

A.1 SLEEP ROC .. ......................................... A.1-1A.2 Purchase Description for 3-kW Stirling Engine .. A.2-1I, ;~!t*A.3 MIL-STD-133B..........................................A.3-1

APPENIX BEXCERPTS FROM MIL-STD-810B AN~D MIL-STD-705 B-

B.1 iliaryRequirements for Mechanical Testing of3-(.WGenraorSet. .. ............................... B.l-1

SB.2 Military Specifications For Long-Term StabilitySTests .. ............................................. B.2-1

~.. ,~APPENDIX C SPECIFICATIONS FOR STANDARD FAMILY UNITS .. C-i

CAl MIL-STD-633C. .. ..................................... C.1-1C.2 MIL-STD-633E-14 .. ................................... C.2-1

4 ix

LIST OF FIGURES

NUMBER PAGE

1-1 Alternative Configuration for Stirling Engines . . . . . 1-3

1-2 FPSE Reliability-Oriented Features ..... ......... ... 1-41-3 FPSE Units Developed and Tested at MTI ..... ..... ... 1-62-1 Technology Demonstrator Engine Layout ...... ...... ... 2-32-2 MTI l-kWe Technology Demonstrator Engine ..... .... .. 2-42-3 Heat Exchanger Layout ............. .......... ... ... 2-62-4 Combustor System Layout .......... . . 2-92-5 MTI 3-kW Prototype Engine ........ .......... . 2-11

e

2-6 Combustion Rig . .. .......... ..... .. 2-132-7 Linear Motor/Generator Test System..... ... 2-15

2-8 Engineering Model in a Package Unit on Test withTemporary Combustor...... ........... ....... . . . . 2-17

2-9 EM Engine/Alternator . ............... . 2-183-1 Comparison of Physical Parameters . . ...... . 3-43-2 MTI 3-kW Engineering Model System . . ...... . 3-53-3 Major Components of EM System ....... .... . 3-63-4 ADP Projected System Configuration . ... . 3-93-5 ADP Configuration . . . . . ............. 3-10

3-6 EM Unit Weight Distribution ..... .............. 3-133-7 Lightweight 3-kW FPSE/Alternator ........... 3-14e3-8 Orientation Capability of the EM System .... ......... 3-193-9 Orientation Capability for the ADP ..... ........ ... 3-203-10 Total Cycle Efficiency ..... ..... .............. ... 3-263-11 Alternator Peak Efficiencies .......... .......... .. 3-273-12 Combustor Peak Efficiencies . . ...... ..... 3-2823-13 Exhaust Plume Temperature Calculation ...... ...... . 3-343-14 IR Signature for the ADP ..... ... ......... ... 3-35

3-15 Temperature Measurements of Exposed Metal on FPSEs . . . 3-373-16 TDE Emissions Using Natural Gas: Volumetric Parameters. 3-433-17 TDE Emissions Using Natural Gas: Mass Parameters. . .. 3-44

3-18 TDE Noise Measurement ................ 3-49

3-19 MTI 3-kW Engineering Model Package ..... ......... . 3-50

xi

-NMO PA k.AI4Ji-*r fIa"

T-7~

LIST OF FIGURES (Cont'd)

NUMBER PAGE

3-20 TDE Thermodynamic Power Output ..... ............. 3-573-21 Endurance Test Results -TDE ....... ............ . 3-563-22 Frequency Versus Time ........ .............. . . 3-753-23 Load Voltage rms Versus Time . . . .......... 3-76

3-24 Alternator Voltage Wave Form ..... .......... . . 3-773-25 Alternator Voltage earmonic Content .... ...... .... 3-783-26 Transient Response Predicted for Engine Sys.em ParameterI

for Step Load Change from Full Load to 20% Load . . . . 3-833-27 Transient Response Predicted for Engine System Parameters

for Step Load Change from 20% Load to Full Load . . . . 3-844-i Comparison of FPSE Characteristics With Other Military

Generators ...................... ......... 4-8

4-2 FPSE Development Status Timetable ... ........... .... 4-11K 5-1 Lightweight Alternator Development Schedule ...... 5-3

5-2 FPSE Advanced Development Prototype System DevelopmentProgram Schedule ....... ....... ................... 5-6

xI

xii

"LIST OF TABLFS

NUMBER PAGE

3-1 COOLING SYSTEM SPECIFICATIONS ..... ............. ... 3-83-2 FNGINEERING MODEL, SYSTEM WEIGHT BREAKDOWN .......... ... 3-12

3-3 CONTROL SYSTEM ELEMENTS AND PROJECTED ADP REQUIREMENTS. . 3-163-4 FPSE DESIGN ELEMENTS AND POSSIBLE WEIGHT REDUCTION. . . 3-17

3-5 DESIGN CHANGES REQUIRED TO ACHIEVE WEIGHT GOAL .... ..... 3-173-6 COMPARISON OF THERMODYNAMIC PARAMETERS ........... .... 3-243-7 TDE MEASURED COMPONENT EFFICIENCIES ... .......... .... 3-29

3-8 TDE MEASURED SYSTEM EFFICIENCIES............. 3-293-9 PARAMETERS FOR THE COMBUSTOR AIR BLOWER AND ATOMIZER. . 3-30

3-10 3-kW EM SYSTEM EFFICIENCY DESIGN TARGETS .......... .... 3-32

3-11 ADP PROJECTED EFFICIENCY ..... ................ ..... 3-32J 3-12 RANGE OF LIQUID FUEL PROPERTIES .... ............ .... 3-403-13 TDE MATERIALS LIST ......... ..................... . 3-52

3-14 i'ROTOTYPE ENGINE MATERIALS LIST .... ............ .... 3-53*"3-15 EM MATERIALS LIST .......... ...................... 3-54

i 3-16 COMPARISON OF OPERATIONAL PARAMETERS ............. .... 3-563-17 CALCULATED FUEL CONSUMPTION IN VARYINr" CLIMATIC AND ALTITUDE

CONDITIONS FOR THE EM SYSTEM ....... ......... .... 3-62

3-18 SOLAR-FIRED 15-kW FPSE RELIABILITY STUDY ........... ... 3-693-19 FPSE ELECTRICAL PARAMETERS VERSUS REQUIREMENTS .... ...... 3-723-20 ELECTRICAL VERFORMANCE CHARACTERISTICS OF AC GENERATOR

SETS ............... ........................... . . 3-73

3-21 ENGINE-GENERATOR SPECIFICATIONS .... ........... .... 3-74

3-22 STEADY-STATE VOLTAGE VARIATION DATA ... ......... .... 3-77

3-23 VALUES FO MAXIMUM DEVIATION FACTOR .... .......... .... 3-80

3-24 STEADY-STATE, VOLTAGE HARMONIC CONTENT TEST DATA. . .... 3-82

3-25 TRANSTINT REISPONSES FOR THE EM SYSTEM ... ........ .... 3-85

4-I. MEIAI)COM STUDY, COMPARATIVE RESULTS ... ......... .... 4-2

x 1 ii

SECTION L.O

INTRODUCTION

4 1.0 INTRODUCTIONThis document comprises the final report of a study to project the capabilityof free-piston Stirling engine (FPSE) generators to meet military require-ments for mobile electric power. The study was conducted by MechanicalTechnology Incorporated (MTI) for the Army's Mobility Equipment Re~earch andDevelopment Conmmand (MERADCOM) under contract DAAK70-81-C-0115. The conclu-sion of this report is that the FPSE can, with continued development, meet[ or exceed all of the military requirements for 3 kW silent tactical genera-tors operating on military logistic fuels.

'it1.1 Background

In 1969, MERADCOM published a report detailing the results of a survey thatwas conducted "to critically review the entire silent, power generationNItechnology field." 1 The purpose of the survey was to provide guidance forprogram planning in the early development of reliable and silent military

ground power sources. A Stirling-cycle engine-generator was among the candi-date energy conversion systems considered in the survey. Regarding Stirlingengines, the report commented that "the hardware is a complex mechanicalsystem requiring strong design discipline in order to seal the working fluidand maintain good control over the system under dynamic operating conditions."

Since 1969, significant advances have been accomplished in Stirling enginetechnology that address the identified limitations reported. Most notably,

L' the reduction to practice of the FPSE in the early 1970s provided a simple,

hermetically sealed, gas lubricated design with the potential for a longlife and high reliability. Additionally, the FPSE is characterized by thesame attractive operating features that are common to most Stirling engines:high efficiency, multifuel capability, and quiet operation.

1.2 Technical Concept

MTI is developing the FPSE for a variety of commercial product applications.

The basic design approach for FPSE integrates power cycle machinery and loaddevices within a single hermetically sealed unit. Integration of the engine

"'A Silent, Electric Power Generator for Tactical Applic tions Special Study,"US MERDC, Ft. Belvoir, Virginia, June 1969, Report 1954.

1-1

S section with a linear alternator load is illustrated in Figure 1-1(a) and

is compared with the more conventional Stirling engine rotary alternatorconfiguration shown in Figure 1-1(b). FPSE generator configurations operatewith only two moving parts that utilize working fluid gas springs to con-trol their prescribed motions. These two dynamic components, the displacerpiston and the alternator piston, are supported on gas bearings. The gasbearings provide a working fluid gas lubrication for the moving surfaces.As a result, all surface contact is eliminated during engine operation.These design features provide the FPSE with an inherent potential for achiev-ing long life with a high degree of reliability. Figure 1-2 schematicallyillustrates the engine's reliability-oriented features.

In addition to an inherent potential for durability, the FPSE achieves highefficiency over a broad operating range. Theoretically, the power cycleefficiency is equal to the Carnot efficiency for an equivalent set of oper-ating temperatures. In practice, nearly 70% of Carnot efficiency can berealized through good design technique. In the low-power range (

Heater Hot Space (Expanson)I -.-- (Heat Added)( " Regenerator

(Heat Stored& Released) Displacer Piton

Cooler' * (Heat Cold SpaceRejected) (Compreasion) RotaryNRjetd Alternator

Displacer PistonPower Piston

Oliiubri .,te

Lisser~~~Div Alenaoaft McansLto Load

S~Drive MocuanimLinew Alternator 11!

(a) Free-Piston Stirling (b) Conventional Stirling

Fig. 1-,. Alternative Configuration for Stirling Engines

793494-3

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'am

OltI

.3 14

.1.14U,0

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1-4

A number of FPSE units have been developed and tested at MTI since the mid

1970s. Some of these units are shown in Figure 1-3. The state of the art

of the FPSE is MTI's 3 kW Engineering model Engine Generator. The Engi-

neering Model can currently be classified as a nonsystem advanced develop-

ment prototype.

1.3 Militarization Study

By virtue of its unique operational capability, the FPSE offers potential

advantages of a strategic and logistic nature to users of mobile power

equipment in a military environment. For this reason, MERADCOM contracted

MTI to perform an assessment study of the suitability of the FPSE for meet-ing the military's need for ground power. The program objective was toutilize test data and design calculations to project the capability of theFPSE to meet military requirements for tactical. generator sets. The work

scope consisted of two major tasks:Task 1.0 Design EvaluationTask 2.0 Development Plan

The purpose of Task 1.0 was to compare FPSE test and design data with suit-

able military standards and specifications. Task 2.0 involved the prepara-

tion of a development plan to achieve full demonstration of FPSE generator

systems operating on military logistic fuels to provide the electrical power

output performance as-defined in MIL-STD-1332B. The study was accomplishedin four months. The following sections detail the methodology that wasemployed and the results that were achieved.

1-51-5

L , "\ *

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04

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44

ILI1-6

1- illiII

-.... . . . . . .

mllTION 2.0

* METHODOLOGY

IIII

b IA

* . - ... -. . U..-

2.0 METHODOLOGY

The Task 1.0 effort comprised the major portion of the study. As stated,the task objective v'as to compare FPSE test and design data with existingmilitary standards and specifications. The following military documentswere considered:

1. Purchase Description For Low Noise 3.0 kW Stirling Engine Power Plant,

MERADCOM, March 28, 1974. Included were the following reference

documents:

MIL-G-3056: Gasoline, Automotive, Combat

MIL-T-5624: Jet Fuel, Grades JP-4 aud JP-5

MIL-STD-810: Environmental Test Methods for Aerospace and

Ground Equipment, Miscellaneous

"MIL-STD-1472: Human Engineering Design Criteria for Systems,4 Equipment, Facilities

MIL-STD-1474: Noise Limits for Army MaterielVV-F-800: Fuel Oil, Diesel

2. MIL-STD-1332B. Definitions of TUctical, Prime, Precise and UtilityTerminologies for Classification of the DOD Mobile Electric PowerEngine Generator Set Family, March 13, 1973. The following referencedocuments were considered:

MIL-STD-633: Mobile Electric Power Engine Generator SetFamily Characteristics Data Sheets

MIL-STD-705: Generator Sets, Engine Driven, Methods ofTests and Instructions

Appendix A contains a replication of these doc'ments. For the purpose of

this study, all information that was derived from the above documents was

categorized as a military requirement even though, as in the case of thePurchase Description Document, the term requi-ement is not exact.

The following three subsections contain a description of the approach that

was used to complete each of the following subtasks:

2-1

." - 1 , _ .

Subtask 1.1 Test Data Comparison with RequiramentsSubtask 1.2 Design Data Comparison with RequirementsSubtask 1.3 Projected Design Comparison with Requirements.

2.1 Test Data

The primary sources of FPSE test data for Task 1.1 were MTI's TechnologyS'V Demonstrator Engine (TDE), MTI's "Prototype Engine", and component test

rigs. Each of these hardware systems was used for exploratory developmentat MTI, and they formulated the .tate of the art for the FPSE during theI course of the study.2.1.1 Technology Demonstrator Enzine (TDE)The TDE is MTI's 1.0 kW FPSE research engine. The engine was developedunder a contract with DOE and is currently used as a tebt bed engine toadvance the state of the art of FPSEs. By far, the greatest amount of test

r data obtained for this study was from the TDE.

The TDE, shown schematically in Figure 2-1, consists of the following majorcomponents:

: Free-piston Stirling engine (FPSE)* Natural gas-fired external heat systeme Linear alternator* Controls and auxiliaries.

The TDE was designed to meet the following specifications:

E Electrical power output - 1.0 kWe Operating frequency 4 45 Hz* Engine shaft efficiency 730Z.

This engine system was originally designed and built during 1978-1979 andis equipped with the extensive instrumentation necessary for engine perform-ance evaluation. Figure 2-2 shows the TDE on its test stand.

2-2

V ~ k~~4 -- -.. - -

..... - .... . . . ... . .. . . _ . .. ...... . .. i " ,-

f Fuel Nozzle

SAir .

Inlet4...oxhiust

PreheaterCombus t ion

h" Chamber

Epansion_ _

Spacenio Burner Liner

, Ha:ew j.Heater Head

(internal) -DisplacerRegenerator Cooler

Displacer compressionod Spaces

Displacer,Ga Sprinlg

Compressior Spac$Connector Duct

Blearinu Power PistonAlternator Plunger

VesselAlternator Stator

Bearing

Plenum ,

Bounce Space

PistonGas Spring

aimS

Fig. 2-1 Technology Demonstrator Engine Layout

2-3

r7-2-4

E dk -05

2.1.1.1 Engine. The TDE is a free-piston displacer type, or ganma engine,

R which is thermodynamically similar to conventional Stirling engines exceptthat the piston and displacer motions are controlled by the resonant sp.ing-mass system rather than a fixed mechanical linkage.

The rmodynamics. ' The thermodynamic elements of the engine consist of an expansion space and

a compression space that are connected by three heat exchangers: the heater,regenerator, and cooler. The function of the thermodynamic system is toconvert thermal energy into mechanical energy at high efficiency. The ex-pansion space is the volume enclosed by the displacer hot end and cylinderhead. The compression space is actually two contiguous volumes. In one, the

displaced volume is due to motion of the displacer cold end; in the other,the dLsplaced volume is due to piston motion. The compression space is

"isolated" from the expansion space by a clearance seal at the cold end of

the di.;lacer and from the "bounce" chamber by clearance seals around the

power pirron and displacer rod.

Heater

The heater head is a monolithic pressure vessel design which is integral

with the annular regener-tor pressure wall; see Figure 2-3. This designrequires no high-temperature structural weld or brazed joints.

The internal heater is iwmnediately adjacent to the expansion space. Rec-

tangular flow passages and fins are machined into the inside heater pressure

wall to enhance the heat transfer process. The inner heater wall is a thin

shell which separates the heater from the expansion space. This liner ex-

tends past the regenerator down to the cooler. The outside of the pressure

wall has been finned to augment combustion gas heat transfer to the head.

* Regenerator

The regenerator is an annula. porous ring located between the heater and

cooler. The regenerator removes and stores thermal energy from the gas as

2-5

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it flows from the heater to the cooler and adds energy to the gas as itflows from the cooler to the heater. The outside regenerator wall is partof the engine pressure vessel and is, therefore, subje to hS.,h internalpressure. There is a large thermal gradient along the length of this wallwhich contributes to the stress level, The wall is tapered to reduce con-duction losses by taking advantage of higher material strength at the cold

"e ,end of the wall. The annular regenerator matrix is made up of individualwoven screens made of 1 mm wire and lO0-by-lO0 mesh. The inside wall(displacer cylinder wail) is a thin walled tube which is designed to preventshort circuiting of the neater and regenerator.

Cooler

The cooler, located in an annulus between the regenerator and compressionspace, rejects he-t from the thermodynamic cycle to a closed loop hydronicradiator. The cooler has finned flow passages on the helium side and on the

water side. The water side fins also transmit the helium working pressure

to a structural cylinder, thus reducing the required thickness and causing a/ temperature drop in the

wall. The cooler helium volume is connected to the

compression space volume through the compression space connecting duct.

Dynamics

The TDE has two dynamic components: the displacer and the piston. The

dynamic components iw~pose volumetric boundary conditions on the thermo-

dynamic working space, while the thermodynamics impose pressure forces onthe dynamic elements.

Displacer

The displacer is guided in the engine cylinder by a gas bearing on the dis-placer rod. The displacer gas bearing system has demonstrated noncontacting

operation between the rod and bearing sleeve. The displacer mass is dynam-

ically coupled to the engine frame by a gas spring designed to balance thenet displacer inertia. The pressure difference across the heat exchangers

Impose a load on the displacer. The power required to drive the displacer

2-7

is supplied by the thermodynamic cycle pressures acting on the displacer

rod area.

K ,Power PistonThe power piston subassembly is the remaining major dynamic element andconsists of an engine piston, alternator plunger, gas spring piston, andgas bearing journals. Most of the engine thermodynamic power is deliveredto the alternator via the power piston. A piston gas spring is designedto balance the net inertia of the piston subassembly. The power piston isradially supported on either side of the alternator plunger by inherentlycompensated hydrostatic gas journal bearings.

Gas Springs

The power pLoton and displacer gas springs provide a portion of the springfotce required to resonate the piston and displacer mass at the desired fre-quency. The gas springs, to the first order, undergo adiabatic processes, al-though thermal hysteresis, seal leakage, and mid-stroke port leakage resultin nonideal spring behavior and losses. The gas springs are provided withmid-stroke ports that provide make-up of net seal leakage flow. These mid-

stroke ports stabilize the axial locations of the displacer and power pistons.

The capability of the power piston gas spring to function as the bearing

supply compressor is included in the design. A check valve is located be-r tween the gas spring and the bearing supply plenum. As the pressure in the

gas spring rises above the bearing plenum pressure, the valve opens, supply-ing gas to the plenum. The gas removed from the spring is made up by mid-

stroke port flow.

2.1.1.2 Combustion System. The combustor system consists of the followingmajor components: (See also Figure 2-4)

0 Preheater

* Fuel nozzle/swirler cup

* Combustion chamber linerI Tgniter

* External heater head.

2-8

S ..

w04

w 1

'2-9

The fuel and air are supplied to the combustor from an external fuel/aircontrol sys tern. The inlet air is preheated by the combustion exhaust in afolded foil preheater. The preheated air enters the combustion chamberthrough a swirler cup to create a turbulent mixing zone. The fuel is in-jected through the center of the swirler cup into the combustion zone. Thecurrent combustor system is desigaed to burn natural gas at a peak firing

e rate of 60K Btuh.

2.1.1.3 Alternator. The alternator, which provides the mechanical pistonload, is a flux-switching linear alternator. The basic alternator designis an adaptation of several linear motor designs developed for other M4Iprojects. The DC coil in the stator provides the basic circulating flux.The moving plunger completes the magnetic path around the DC coil and switchesthe flux across the double-slot AC coils. The compensating coil in the poletips on the plunger reduces the AC flux in the plunger$ which reduces the in-ductive reactance of the machine.

The magnetic iron in this machine was fabricated of radially oriented lamina-tions made of Hyperco-5O. This material saturates at a higher flux densityand has lower eddy losses than conventional magnetic iron. The Hyperco.'50was selected to provide alternator efficiencies in excess of 90%. This high

level of operating efficiency was required for the originally intendedapplication - isotope source space power systems.

2.1.1.4 Controls. During normal operations, the engine/alternator systemis controlled by two primary control systems: the heat input, or combustor

control system; and the power output, or field control system. The former

is used to control heater head temperature and the latter to control enginestroke. Both control systems are used for experimental purposes and operate

manually.

2.1.2 "Prototype Engine"

The "Prototype Engine" was built under MTI's privately funded product devel-

opment program. The engine is shown on its test stand in Figure 2-5. The

prototype engine incorporated a unique design approach involving a diaphragm

2-10

Its

Fig. 2-5 MTI 3-kW Prototype Engine

e

2-11.- 207

displacer drive system. Unfortunately, the engineering difficulties encount-e red, while attempting to achieve reasonable levels of power output, more thanoffset the intended enhancement in engine reliability. Some of the problemsassociated with diaphragm displacer engines include unavoidably large deadvolumes, large heater head structures, and excessive material cost - to namea few. originally designed to be a 3 kW engine, it failed to develop ratedpower due to the inherent difficulty associated with scaling diaphragm dis-

placer engines. Furthermore, cost projections showed that engine manufacturewould be expensive. Based on this experience, the diaphragm engine designa pproach was determined 'jy HTI to be inappropriate for power levels above 1kW,and was subsequently abandoned. The "prototype"' engine did, however, operatesuccessfully at part load and as such operational and design characteristicsof the "Prototype Engine" are cited in the test comparison results listed in

Section 3.0.

2.1.3 Component Test Rigs

Two major component test rigs are used to support FPSE development at MTI.One of these rigs supports combustion system development and the other,alternator development.

The combustion rig, shown in Figure 2-6, consists of a fully instrumentedfree burning combus tor test stand that is used to evaluate combustion pro-cesses and characteristics such as efficiency, temperature profile,emissiotl3, adfmestability.

The alternator test rig is a vibration motion amplifier that has the capa-bility to test alternators up to 20 hp and at strokes of 1.0 inch at fre-quencies of up to 60 Hz. A picture of the alternator test rig is shown inFigure 2-7.

2.2 Design Data

Under its FPSE product development program, MTI is developing an advanceddevelopment prototype system called the Engineering Model (EM). During thecourse of this study, most of the EM component designs were completed, somewere already fabricated, and still others were undergoing initial testing.

2-12

4.4

..4. jIf

4 I.p414

I2-3

.4.. . S .

ElectrodynamicShaker

Fig. 2-7 Linear motor/Generator Test System

PRCSZMO PAU& AIAmMO'2-15

The EM, therefore, represents the state of the art in FPSE design and wasused as a source of design data for comparison under Task 1.2 of this study.

Furthermore, since the EM desib" is fixed but not yet fully fabricated, it

formulates a precise definition of the term "design data", as interpreted inthis study. Additionally, it provides a clear distinction between the designdata and the design projection evaluated under Task 1.3.

2.2.1 The Engineering Model System

2.2.1.1 The Engineering Model Engine/Alternator System. The EngineeringModel is a full packaged self-contained 3 kW dieuil fuel fired generatorsystem built around the engineering model engine/alternator unit. The systemis designed to provide 120 V, i, 60 Hz power quietly, reliably, efficiently,and with excellent regulation. Ease of operation, ruggedness, and minimalmaintenance are specified design goals. The power control system, a criticalelement of any free-piston generator system, is designed to provide thetransient response and steady-state regulation capabilities. The systemincludes the following major subsystems:

e Combustore Combustor control systeme Engineering 'model engine/alternator unit

o Cooling system

e Power control system.

The EM system is envisioned in its packaged configuration in Figure 2-8. Adescription of the engine/alternator unit and the power control system are

provided below.

The EM Engine/Alternator Unit

The EM engine/alternator unit is a single cylinder free-piston displacer

type engine driving a "partially saturated plunger" linear alternator. The

EM is shown with a temporary, oversized combustor unit in Figure 2-9. The

complete EM will have a compact combustor and will be about two thirds thelength of the unit shuwn in Figure 2-9. The engine utilizes only hydro-static gas bearings and clearance seals in its displacer and piston drive

system for long life and high reliability. The basic engine layout and

2-16

Ijl- I

\ ~"4,

II

2-17

I I. q

ILI

Fig. 2-9 EM Engine/Alternator on Test with Temporary Combustor

2-1S

structure are extensions and improvements of the work accomplished with theTechnology Demonstrator Engine. The engine is composed of three major com-ponents and subsystems:

*, * Heater head

e Displacer system

e Alternator system.

The heater head for the engineering model is a monolithic nickel-based alloycasting with integral internal and external fin geometries. It is a simplerugged component designed to provide a rated power operating life of greater

than 10,000 hours.

The displacer drive consists of the displacer body and dome, fully gasbearing displacer rod, and displacer gas spfings. The displacer body con-tains the displacer cylinder clearance seal. The displacer drive system andthe resulting dynamics are critical to the performance of the engine powercontrol system. As such, a proprietary design innovation has been implementedto ensure that the displacer achieve a desirable dynamic state.

The linear alternator consists of a 0.5 inch thick cylindrical plunger

which reciprocates between inner and outer cylindrical stators. A DC fieldcoil generates a toroidal flux path linking both the inner and outer stators.The toroidal flux path passes through the two magneti'cally active rings onthe plunger in passing into and out of the two stators. Consequently recip-rocating the plunger causes the flux toroid to move axially along the stator.As it does so, its sinusoidally links and unlinks four physically separateAC output coils. The AC coils are electrically connected and act as onesingle output coil providing alternating AC voltage and power.

This above linear alternator configuration is referred to as a "partiallysaturated plunger" alternator because of the magnetic characteristics of theplunger design. It was chosen for the engineering model because it is rela-tively rugged and has a low plunger weight. The light plunger weight

allows operation of the EM at 60 Hz without the use of an auxiliarypiston gas spring, resulting in the potential for a'!hieving a higher over-

all efficiency.2-19

As configured for testing during the 1982 time frame, the EM will have thefollowing specifications:

* Overall efficiency M 25%* Rated net electrical power output - 3.0 kW9 Charge pressure 60 bar"e Heater head temperature 1400F

* Ambient air temperature 95 0F.

2.3 Projected Design

As stated, the EM represents the state of the art of FPSE technology that"has yet to be verified through system testing. The EM, however, wasdesigned for civilian commercial applications and could not be expected tomeet military requirements fcr ground power in every respect. The variance,then, between the EM and military requirements formulates the basis formaking design projections to determine the level of difficulty involved inmodifying the EM system to meet those requirements. Hence, all projecteddesign calculations were based on using the EM as a reference design towhich evolutionary changes or design extensions could be made. Items in-volving significant technical advancements are identified as such. Theprojected design is referred to as the Advanced I)evelopment Prototype (ADP).

2-20

*-W -

*1 7--

SECTION 3.0 -

PARAMETRIC COMPARISON WITH REQUIREMENTS

"~'~m7M

3.0 PARAM4ETRIC COMPARISON WITH REQUIREMEN4TS

The military requirements for ground power were identified from each of thereferenced standards and specifications documents, and were further assembledinto the following separate categories:

e Physical* Thermodynamic

* MaterialaOperational

*Electrical.

Suitbleparameters were then selected for each category to enable a quanti-fiale vauatonof test lata, design data, and designprjcintbemd

relative to the requirements. This section details the results of that para-metric comparison.

3-1

-,- -U A.,

... .. . .. .

SUBSECTION 3.1

PHYSICAL PARAMETERS

...........

`7F&. 3.1 Physical Parameters

Physical parameters were identified as the nonoperational system parameters

including size, weight, orientation, and shock and vibration. A summary of

the physical parameters comparison is listed in Figure 3-1. As indicated,

both the system size and weight would have to be reduced for the projectedAdvanced Development Prototype (ADP). In fact, technology advancement is re-quired to advance the state of the art of linear alternators to achieve light-

weight design capability.

3.1.1 Size

Requirements

The purchase description for a 3 kW Stirling engine power plant requires that

the total system volume not exceed 12 cu. ft.

Test Data

alternator unit has an overall length of 53 in. and an overall diameter of

19 in. yielding a total. vo~ume of 8.7 cu. ft.

The 3 kW "Prototype Engind' has an overall length of 40 in. and an overalldiameter of 12 in.

Design Data

The EM system, as configured in Figure 3-2, has an overall volume of 14.5 cu.

ft. The EM, however, is being designed for laboratory development requiring

easy access of components and space for instrumentation.

The orthogonal views depicted in Figure 3-3 indicate the locations and rela-

tive sizes of the major system components. The engine unit and control system,which account for the largest single volume elements, are 2.5 cu. ft. andJ

2 cu. ft respectively. The coola..t system radiator has dimensions of

24 in. x 17 in. x 2.25 in., accounting for an additional 0.5 cu. ft.

3-3

...... ~ ....... .

V SI

cvn

Q V4)

40

C14

E 00

L3-4

+ ...i ++ i+Iiii i~iiiiiii~i i~ i +i~ i ii~mi ..+ + + . .+ .1.. .. ........ +++ -+ : +A

+ ;o

+ +OD

i,+++ + r l im I

'.

j3-5

4 cJ, . .. . + . . . . . . .. _ +

,ii

44

ii

tt

3-6

3-b

Projected Design

A volume of 11.5 cu. ft. is projected for the ADP. This projected volume re-duction was accomplished by improving the design of the coolant radiator and

control system, and by implementing a packaging scheme that is more appropri-ate for a commercial system. Details of the cooler radiator system redesign

are given in Table 3-1. An air-cooled engine design is also being considered.As indicated, the size improvement is achieved at the sacrifice of additionalparasitic power required. Improvements to the control system are listed under

the next section discussion on system weight. The projected system configu-ration for the ADP is depicted in Figures 3-4 and 3-5.

3.1.2 Weight

Requirements

MIL-STD-1332B requires that the maximum dry weight for a 3 kW generator setnot exceed 300 lb. (Maximum dry weight is the weight of the generator setless fuel, coolant, lubricant, electrolyte, and optional equipment as speci-fied in MIL-STD-633.)

Test Data

The I kW TDE has an overall (nonsystem) weight of 482 lb. The subassembly,.i weights are:

CombusLor 42 lb

Alternator 75 lb (inclUdIng the alternator pressure vessel)Total 482 lb

The 3 kW "Prototype Engine" has an overall weight of 466 lb. The subassembly

weights are:

Combustor 71 lbEngine 130 lbAlternator 265 lb (including the alternator pressure vessel)Total 466 lb

3-7

rS

U -

444

4.P4

0 N 0%C mm 1141" 6N N 0 1 a 0 *0V4 .

P4 r%4-4 *4

44 .0 N.4

I'0 AM 4

0 N C ON . r4 kS . N ~4 N. 00 004

*1.4H A 4

44. 44

44 w

44 A

JA4w

.0i

44 Ii 43-8

3 1. Coutuator

3. Alternator

Top Vie

_-_

Side Vi/w\n d " -

/]

3-9

r.. . . . .. . .. . 2. pi...e

S- 3. Ate 23.5

Side View End Vi---

S- - - - ..,. ---a,...... ~--

44

U.'

LM8

eU.

3-10

Design Data

The Engineering Model System has a total design weight of 485 lb, and iscomprised of the subsystem weights listed in Table 3-2.

The EM unit and controls account for over 88% of the total weight. The EMunit, however, was originally designed as a stationary engine for residential

application without being overly concerned for engine /alternator weight. (Figure3-6 shows the weight breakdown accounting for the EM unit.) It should be notedthat the control system and auxiliaries consist of laboratory-class hardwarethat has not yet been value-engineered for a production unit.

Proj ected Design

The EM system was designed as a laboratory demonstrator of a commercial sta-tionary power generator for which low weight was not a major criterion.Nevertheless, low weight is an important criterion for military power plants.Therefore, the projected ADP design concentrated on achieving the 300 lbmilitary specification.

As indicated in Table 3-2, two major subsystems account for two-thirds of thetotal EM system weight - the linear alternator and the control system.

In kocpIng with the need for improvement in linear alternator specific puwer,

a detailed investigation of the FPSE generator system was made and an advanced

lightweight linear alt~ernator was designed under the MTI product development aprogram. This advanced alternator, based on proven motor technology, will

result in an overall system weight reduction of 111 lb. Figure 3-7 depicts

the envisioned lightweight ADP engine-generator configuration. The figure

indicates the volume (and mass) reduction provided by the lightweight alter-a nator concept.

The control system is the second major subsystem that was examined for poten-tial weight reduction. Because ti~ie EM control system has not yet beenfabricated, nor completely detailed, it is difficult to project the ultimateIcontrol system design. Nonetheless, there is some basis to speculate that

t~io f~inal configtinition could weigh substantially less than the present EM

3-11J

iri

TABLE 3-2

EZGINEERING MODEL, SYSTEM WEIGHT BREAKDOWN["Subsystem Dry Weight (ib)Combustor 42

Engine 61

Alternator ComponentsPlunger 6.5SStator 118.5Press. Vessel 60Adz.ptor Plate 26

Total Alternator System 211

Cooling System 13

Fuel System 12

Controls & Auxiliaries 116

Frame 30Total EM System 485

3rI

'2ii 3-12

Combui to r

(42 ib)

Head (20 lb)Dynamic (5 1b)

k. Cooler

Displacer

Alternator System

-4 Fig. 3-.6 E.M Unit '7eight, Distribution

3-13

''N

-Present AlternatorDesign Envelope

U. I ,' / ii

Fig. 3-7 Lightweight 3-kW e1,7SE/Alternator

3-14

.... .....

V.a-

* control system components. Specifically, three items could result in sub-stantially lower control system weight. Table 3-3 lists the control systemelements as specified for the EM and compares these with projected require-mnents for the ADP. As indicated, the three components of specific interestfor weight reduction are the starter battery, the power supply, and thecapaci tor.

The FPSE starts quite easily requiring only small amplitude displacer oscil-lation and a warm heater head to produce positive power output. Therefore,it is possible that a lower power energy supply would be used for start-up.

Commercially available power amplifiers utilize heavy magnetic components toprovide the proper signal filtering characteristics. Due to the high mnag-

that much of thp power supply magnetics could be eliminated, thereby reducing

system weight by nearly 25 lb.

A capacitor is required for the EM control system to compensate for the in-4' ductive reactance associated with linear alternator field coils. The ADP,

however, would employ a permanent magnet type of linear alternator that mightnot require capacitive compensation in the control system. Elimination ofthe capacitor would save an additional 25 lb in total system weight.

Other design areas that show potential for weight reduction simply involve aconscious effort to eliminate unnecebsary mass. The following FPSE design

elements, shown in Table 3-4, have been identified for possible weight reduc-tion in the ADP.

In total, the ADP system can be designed to meet the militiry specificationfor maximum weight. Table 3-5 indicates the design changes required from theEM to the ADP to achieve the overall weight goal of 300 lb.

3-15

TABLE 3-3

CONTROL SYSTEM ELEMENTS AND PROJECTED ADP REQUIREMENTS

Weight for Weight forEM Design ADP Design

r Electronic Control 4

"Current Sensor

Parasitic Load Switch 54

Power Supply 35 10

Auxiliaries 20 15

Battery 10 5

Electronic Power Supply 5 5

Converter 15 12

Transformer-Rectifier-Filter 6 5

Capacitor 15

Total 116 61

3-16

I; . .TABLE 3-4FPSE DESIGN ELEMENTS AND POSSIBLE WEIGHT REDUCTION

FPSE Design Element Weight Reduction (ib)

Combustor - 7

Displacer Drive - 5Heater Head - 1Displacer Post -1

Total -14

Tr

S TABLE 3-5

DESIGN CHANGES REQUIRED TO ACHIEVE WEIGHT GOALEM Subsystem Component Weight ADP Subsystem

Subsystem Weight Reduction Weight

Combustor 42 -7 35Engine 61 -7 54Alternator 211 -111 100Cooling System 13 13Fuel System 12 12Control System 116 -55 61Frame 30 -5 25

Total 485 -185 300

3-17

3.1.3 Orientation

Requirements

The 3 kW Stirling Engine Purchase Description requires that the system con-

figuration and the center of gravity shall be such that tipping will not occur

when the unit is tilted 31*.

Test Data

The TDE and "Prototype Engine" have not been configured as total systems.

However, the "Prototype Engine" was operated in both the combustor-up and the

combustor-down positions with no discernible difference in operating charac-

teristics. Furthermore, the gas bearing stiffness is such that the effects

of gravity are small in comparison to the thermodynamic forces. It is, there-

fore, anticipated that orientation will have no effect on the engine/alternator

performance.

Design Data

"The centroid was calculated for the EM system as illustrated in Figure 3-8.A 31* tilt from the horizontal position was considered for the least stable

configuration. Even under the conditions illustrated, a calculated restoring

moment of 1697 in.-lb resulted. Hence, the EM would operate without tilting

in such an orientation.

Projected Design

The centroid for the ADP is shown in Figure 3-9. With a 31* tilt, the ADP

would be stable having a restoring moment of 780 in.-lb.

3.1.4 Mechanical

The mechanical requirements for military generatur sets involve design capa-bility to withstand:

e Drop Test (free fall)* Vibration Test

* Drop Test Ends

* Railroad Impact Test

* Humidity Test.

3-48

)II.i

--, 7 - 77-, 77-

(Maximum Tilt Angle = 410)

Fig. 3-8 Orientation Capability of the EM System

3-19

tie

4 4Q

Ir

(Maximum Tilt Angle - 380)

Fig. 3-9 Orientation Capability for the ADP

3-20

! 1SK, . ,,, " ....... '................ , .... " " . ...- i

The tests required are specified in MIL-STD-810B and MILWSTD-705. Pertinent*-excerpts from these documents are listed in Appendix B.

* Test Data

The available hardware systems are nonsystem prototypes to which the stand-ards do not apply. However, MTI has developed several free-piston. resonantcompressors that were subjected to U.S. Navy drop hammer tests and continuedto operate successfully. Since the FPSE dynamic components are of a construc-tion and operation that arc similar to the earlier resonant compressors, and

since they use the same chrome oxide surface protective coatings, FPSEs areanticipated to withstand U.S. Army shock and vibration tests equally well.

Desiin and Prolected Data

Both the EM and the ADP frames and mounts were sized to survive the specified

military drop tests.

I0.

J4

3-21

L

SUBSECTION 3.2

THERMODYNAMIC PARAMETERS

3.2 Thermodynamic Parameters

Thermodynamic parameters are considered to be all those operational parametersinvolving heat transfer, heat flow, energy conversion and the operation ofassociated systems. Table 3-6 lists a summary of the thermodynamic parametercomparison. As indicated, the projection is for the FPSE to significantlyexceed the requirement for maximum fuel consumption and to meet the require-[ ments in all other aspects.3.2.1 Specific Fuel Consumption

Requirement

The 3 kW Stirling Engine Purchase Description requires that the rated loadfuel consumption of the engine including all accessories necessary to sustainoperation in the generator set not exceed 0.6 lb of fuel per brake horsepowerhour on any of the fuels listed (combat gasoline, JP-4, JP-5, DF-1, andDF-2).

Because the FPSE has the linear alternator integrated with the engine in a

hermetic encasement, a more accurate measure of fuel consumption would include"the alternator efficiency and would be expressed in terms of pounds of fuelper net kilowatt-hour. Assuming that a rotary alternator has typical ratedefficiency of 85%, then the military requirement as specified in the purchase

description would be 0.95 lb of fuel per net kilowatt-hour.

Test Data

The TDE consists of three major subsystems; combustor, engine, and alterna-tor. The TDE is a research system, and, as such, its component subsystemshave not been matched to operate simultaneously at their optimum conditions.

As an example, the alternator was designed to operate at 60 Hz, whereas theengine was designed for 45 Hz. Therefore, taken as a system, the measured TDEperformance does not accurately represent the performance capability of FPSEtechnology. For this reason, two separate sets of measurements are beingconsidered here, to calculate specific fuel consumption (SFC): one based onindependently measured component efficiencies and the other based on measured

system performance.

3-23

i " ~~~~~~~~................... ...... '.................-... .. '................ "

S....... -.2 '"~~ ~ ~ .. ... ..*. .. . . .

~ . -' - ,-r' -w r --, rn---- ..

I'q

c '

ih

t6

In

lop0-30

00I

- O 0

4-2

3-24

,., - ZZ.L - : - : , ' ' .. .I "

Figures 3-10, 3-11 and 3-12 show the measured peak efficiencies for the engine,alternator, and combustor system respectively. The engine/alternator drive(or transmission) system taken as a whole includes the gas springs and gasbearings. This is estimated to be about 90% efficient. Finally, th- TDEoperates with total auxiliary support from the laboratory test cell. It isestimated, however, that a well-designed auxiliary system for the TDE wouldconsume about 11% of the gross power generated.

The measured component efficiencies provide a total of 0.22 for the whole

optimized TDE; see Table 3-7. Based on the above measurements and estimates,the following calculation can be made for the SFC of an optimized TDE.

3413 Btu 1 1

kWh 18,300 Btu/lb (DF-2) 0.22

SFC = 0.85 lb/kWh

"A' Taken as a total system consisting of unmatched components, the best measuredoverall system efficiency is 14% and consists of the measurements listed inTable 3-F. Th, offlclency calculation is as follows:

3413 Btu 1 1kWh 18,300 Btu/lb (DF-2) 0.14

SIC .1.3.1 lb/kWh.

Design Data

The EM has been designed and is being developed as a well-matched system toprovide good overall performance. Additionally the EM will operate as a standalone system providing all of the auxiliary power necessary for self-sustainedoperation. In addition to the cooling system parasitic power of 165 W (de-tailed in Section 3.1.1), auxiliary power is required for the combustor sys-tem's air blower (75 W) and atomizer (60 W). A description of these twocomponents Is provided in Table 3-9.

3-25

is - . - . -

40

PM =40 ba.x = 2.2 cmf = 44 Hz

130 '-2 0,, I ...I I I . . I20

100 200 300 400 500 600Mean Heater Head Temperature (0C)

Fig. 3-10 Total Cycle Efficiency

8 11

,326 82911

120 1800

110 1600I

I, ,

100- 1400

1.205 Amp Field90 35.8 S1 Load -1200

1.625 Amp. FieldS~24.3 n Load

IsIL 70- -800 e

60- 600

1.205 Amp Field50- 35.8 a Load

40- 200

SI .I .. .. ..I I,.00 0.2 0.4 0.6 0.8 1.0

Stroke (in.)

Fig. 3-3.1 Alternator Peak Efficiencies

3--27

# . p ,....... .....

10 * Combustor System EfficiencyS:" "10-A Heater Head Efficiency

9-

8-

7-

Tests: May 6, 1981 4L"May 11, 1981

2- May 15, 1981H H/F m 35-38

0.6 0.7 0.8 0.9 1.0

ES, EH

Fig. 3-12 Combustor Peak Efficiencies

3-28

, ~*. I ,.

low: TABLE 3--7

TDE MEASURED COMPONENT EFFICIENCIES

Subsystem Maximum Efficiency

Combus tor 0.85

Engine 0.36

Alternator 0.90Drive 0.90

Auxiliary 0.89

Total 0.22

TABLE 3-8

TDE M4EASURED SYSTEM EFFICI-2CIES

Subsystem Measured Efficiency (%)

Combustor 0.8

Engine 0.29Alternator/Drive 0.67

Auxiliaries 0.89 (est.)

Total 0.14

3-29

* . , . . . . . . .. . . .. . ..

TABLE 3-9

PARAMETERS FOR THE COMBUSTOR AIR BLOWER AND ATOMIZER

Air Blower

Propeller Diameter 4.2 in.r* Housing Motor Diameter 6.88 in.Operating Speed 16,000 rpmPressure Head 15.7 in. H20Flow 9.86 cfmPower Consumption 75 W

Atomizer Air Compressor

Type 4 vanes swastikaRotor Diameter 2.17 in.Length 1.50 in.Housing I.D. 2.32 in.Operating Speed 1725 rpmPressure Drop 10 psiaPower Consumption 60 W

13

3-30

-. M I. . . . .. .... .. .

"k._ . , ... .. ... .... ..t... ... .. . .. . ... .a ...... . ... ..-- -- -. ... .. . .. .. . .. .... U Mi

The total auxiliary power requirements for the EM total 480 W and consist of

the following:

Cooling System Fan 75

Cooling System Pump 90

Combustor Blower 75

Combustor Atomizer 60@,!Con trolis 180

To lot a]. 480 W

Now, considering both the parasitic power requirements and the subsystem

design goals, the total. EM system efficiency design target is 0,25, as seenv,;in Table 3-10. Tilt following total system performance is cal-culated for the

k .. EM system:

3413 Btu 1 1');+SFC SFC-kWh 18, 3 0 0 Btu/lb 0.25

SFC = 0.75 Ilb/kWh.

SProjected fes1gnOne of the design objectIvws of the advanced development prototype is toimprove upon the EM comlonent efficiencies so that an overall system effi-

ciency of 30% results. The major sources of improvement are expected to berealized In the engine and a.lternator subsystems. It has been determined

that by reducing the alternator flux gap from 0.045 in. to 0.010 in., thealternator efficiency wIll increase from 85 to 90%. On the engine side, anoefficiency Improvement is expected to be realized by decreasing the displacer

drive losses. The overall prnjec ted system ef ficiency and SFC for the ADPIs given in Table 3-11. The calcutat ion for system efficiency follows:

=3413 Btu 1 ____ 6 1kWh 18,300 Btu/lx 0.30

SFC = 0.625 lb/kWh.

3 -3 1

~~~~~~~~~~ -3~.- . . .... ~ .. :~.

-! ,..~ kJ . ~ ~ ~ f.&L,~

TABLE 3-10

-- 3 kW EM SYSTEM EFFICIENCY DESIGN TARGETS

Subsys ternficec

Combustor 0.90eEngine 0.40

Alternator 0.85*Drive 0.97

Auxiliaries & Controls 0.84

Total 0.25

*It should be noted that the high drive efficiency

411 for the EM results from the elimination a majorsource of efficiency loss - the power pistonaft-gas spring.

TABLE 3-11

ADP PROJECTED EFFICIENCY

Combustor 0.90Engine 0.45Alternator 0.90Drive 0.97JAuxiliaries & Controls 0.84

Total 0.30

3-32

-- v .. . . . .. . ..... ... ... .

3.2.2 IR Signature

Requirements

Although no military standard currently exists for power plant infrared (Ik)radiation signature, the intent is to limit the system exhaust plume to a

minimum practical level.

Test Data

Both the TDEs and "Prototype Engines" have a nonsystem research configuration,

which do not accurately reflect IR signature for total systems. Therefore,

no IR signature test data is available.

,. Design Data

A calculation was made to determine the temperature of the exhaust plume ofthe EM system. This calculation is depicted schematically in Figure 3-13.The EM frame is designed as an enclosure to ensure adequate mixing of thecombustor exhaust gas with the warm coolant air. As indicated In Lhe figure,

the calculated exhaust plume temperature is 124 0 F on a 90OF ambient day. To

be detailed in Section 3.5.4, the EM is designed to have a nearly constantperformance independent of ambient temperature. The net exhaust plume forthe EM systeiii, then, wil be 18% above ambient.

Projected Design

The ADIP will have a significantly lower net temperature rise than the EM fortwo reasons:

1. The AIR is more efficient than the EM, thereby requiring less

heat rejected.2. The ADP employs a smaller coolant radiator that produces nearly

twice as much flow as does the EM radiator.

The calculated IR signature for the AI)P is shown in Figure 3-14. As shown,the AIP will have a net temperature rise above ambient of 7oC.

3-33

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3.2.3 Exposed Metal Temperature

Requirement

According to the 3.0 kW Stirling Engine Purchase Description, all partsthat are of such a nature or so located as to become a hazard to operatingpersonnel shall be fully enclosed or so located as to minimize such hazards.

Test Data

In order to verify the low exposed metal temperatures of FPSEs, temperaturemeasurements were taken by placing thermocouples at various locations onthe TDE during operation. The TDE was operating at 60% rated power, and astable operating condition was established for 10 minutes prior to recordingthe temperature measurements. Figure 3-15 shows the results of those measure-

ments. Only the combustor exhaust pipe has a temperature of sufficient de-gree to be a concern to operating personnel.

Design and Projected DataBoth the EM and ADP systems will be configured so that the combustor exhaust

pipe is internal to the overall system package and totally removed frompossible contact with operating personnel.

3.2.4 Multifuel cabtl_

Requirements

The 3.0 kW Stirling Engine Purchase Description states that the engine,burner, fuel supply system, and fuel control system shall be designed tooperate on the following light petroleum distillates:

* Combat gasoline per Specification MIL-G-3056

* Jet fuels JP-4 and JP-5 per SpecificationMIL-T-5624

fA

e Diesel fuels lF-l, DF-2, and DF-A per Specification

VV-F-800.

3-36* . ,

: w -"" ' " t . 9.

!'.II

A IdCombustt

4'

3.....3 7-1

CombustorExhausto Pip

.~.z~rxm 7 21117711TDEFig,. 3-15 'remlpterat.ure, Measurements of Exposqed Metal on FPSEs3-37

Test Data

MTI's experience with fossil-fired free-piston Stirling engines includesthe-TDE and "Prototype Engines" burning natural gas and methane fuels.

Extensive rig testing of the TDE combustion system was conducted usingmethane. The results of these tests, described in MTI Report No. 81FPSE2,

,e indicated:

1. Good ignition and blowout limits, e.g., lean air/fuel ratiolimits of approximately 50 and 300 respectively.

2. Combustor, although designed for 3 kW heat input, is capableof running up to 10 kW.

3. Sufficient combustor volume and acceptable wall temperatures! ~(

_ _ _ _ _ _ _ _

Design Data and Projected Design

The Engineering Model is being designed to operate on natural gas and on dieselfuel. The EM fuel i..apability will be continually improved so that the ADP will

following discussion addresses the design considerations to achieve this cap-

ability. For the Stirling engine continuous combustion system, the relevantphysical, chemical and thermodynamic properties of light petroleum distillatefuels are similar. The key word here is relevant. Fuel properties such asdistillation range, vapor pressure, lead content, octane number and cetanenumber are not of particular concern. For example, the latter two indicateauto ignition temperature requirements for spark ignition (high auto ignitiontemperature to prevent knock) and diesel engines (low auto ignition tempera-ture), which are irrelevant to a continuous combustion process at atmospheric.pressure. For the liquid fuels being considered, the applicable propertiesinclude specific gravity, freezing point or pour point, flame temperature,lower heating value, viscosity and sulfur content. A comparison shown inTable 3-12 of some of these properties reveals the approximate range ofvariation.

The fact that the hydrogen/carbon mole ratio of gasoline, jet fuel and dieselfuel is approximately constant ("4,.8) means that the mass ratio of air/fuelto achieve a given temperature rise is also roughly the same. Thus, a controlsystem which provides a constant air/fuel to achieve a predetermined tempera-ture rise (desirable from a cycle efficiency viewpoint) would be relativelyinsensitive to fuel type if fuel flow control is on a mass basis. If volu-metric fuel flow control is used, the largo! specific gravity variationmust be factored in,perhaps with a simple manual adjustment. Another alter-native would be to use an exhaust gas oxygen sensor to provide feedback to theair/fuel control. Once again, the small variation in hydrogen/carbon ratioamong these fuels results in a fixed relationship between oxygen (or carbondioxide) in the exhaust and air/fuel mass ratio. In summary, it appearsfeasible to use a single control system for the range of fuels listed in the

1urchase description.

3-39

TABLE 3-12

RANGE OF LIQUID FUEL PROPERTIESProperty Maximum Minimum % Difference

Specific gravity (60 0 F) 0.83 0.72 15"Lower heating value (Btu/I.b) 18,500 18,000 3Adiabatic stoichiometric flame (OF)

temperature "'4100 'V0

Kinematic viscosity @ 100F (c.s.) 6 0.5Stoichiometric A/F 14.7 14.5 1Sulfur (weight %) 1.0 0

,,

Ie

3-40

Fuel supply can also be provided by a single system if the pump is designedto handle both low lubricity gasoline and high viscosity diesel fuel. Mostdiesel fuels will have viscosities of 2-3 centistokes at 100*F; fuel vis-cosity will have a -major effect on fuel nozzle atomization. For low ambienttemperature operation it may be necessary to heat the fuel to insure adequatepumpability and atomization, e.g., 6-10 centistokes maximum. Fuel storage

"' could be in the same tank since all of the army fuels are compatible. It may

be desirable, however, to provide separate tanks if long-term storage areask are characterized by aiabl ent temperature extremes.

The combustor itself would also be capable of multifuel operation. The changesin burner wall temperature, which result from increased flame luminosity, i.e.,aromatic content-, could be handled by designing the cooling for the most lu-

nminous or radiant flame DF-2 fuel. Likewise, the fuel nozzle spray character-istics would be based on the most difficult fuel to atomize and ignite; onceagain,DF-2. There should be no significant difference in combustion efficiencyfrom fuel to fuel, i.e., fuel consumption.

Thus, insofar as the engine, combustor, fuel nozzle, air/fuel control and fuelsupply system are concerned, it is feasible to utilize gasoline, jet fuel anddiesel fuel in a single EM design. The possible exception is the preheater.

As sulfur content of the fuel increases (gasoline to jet fuel to diesel fuel)the amount of sulfuric acid in the exhaust products increases proportionately.As long as the acid remains in a gaseous state there is no problem. If,however, the exhaust is cooled below the dew point ("'300*F), a corrosive con-,densate is introduced. If either the average exhaust gas temperature in thepreheater or the local gas temperature in contact with a cool preheater wallIs below 300F, condensation occurs. United Stirling of Sweden experiencewith the P-40 stainless steel preheater has indicated corrosion using dieselfuel but none with unleaded gasoline. It seems reasonable to expect similarresults in the EM burning jet fuel or diesel fuel if a stainless steel pre-heater is used. To prevent this would require reducing the preheater effec-tiveness n using a material impervious to sulfuric acid (possibly ceramics).

3-41

S". ' . ... / 7 ' ~~ ......- .. ...... w.... .. ............ .. ..... ....... ...... 1I.. .. IJ ,. . .. .- ... ...-

To develop an EM Stirling engine system to operate on the military fuelsdetailed in the purchase description will require:

e A fuel nozzle and combustor optimized for DF-2 fuel but capableI: "of satisfactory operation (efficiency, temperature profile,ignition and blowout) on gasoline and jet fuel.

. A liquid fuel control system capable of adjusting to changes"r in viscosity, density and heating value.

e A preheater which is either tolerant of or avoids condensationof sulfuric acid in the quantities contained in diesel fuelcombustion products.

e A fuel supply system which can handle variations in lubricity,

viscosity and density.

3.2.5 Emissions

RequirementsThe purchase description requires that the Stirling engine power plant havea "low air pollution characteristic"..

Test Data

Gaseous emissions (No CO and HC) of the TDE were measured. A total of ninei data points were taken using a matrix of air/fuel ratios (35, 30 and 20 by

volume) and maximum heater head temperatures (400, 450 and 500 *C) burning

natural gas fuel. The results are presented in Figures 3-16 and 3-17, on avolumetric and mas (emissions index) basis respectively, as a function oflambda (X) - X was calculated from the gas analyzer CO2 and fuel composition.The latter is defined as air/fuel divided by the stoichiometric (theoreticalfor complete combustion without excess air) air/fuel.

The following conclusions can be made:

a Small variations in preheat temperature, heater load, and meanhead temperature did not affect the emissions levels.

* As combustion becomes leaner (increasing X) NO decreases and COxincreases as expected.

3-42

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80

70 A

60-

r> 50- 0

'40-

30-

3 Tcontrol

04000C04500CA500C

2u Note: NOX and CO Dry SampleHC (Ref. to Methare) Wet SampleSampling Upstream of Preheater

10-HC

C , I , , I , _"0 2,0 2.5 3.0 3.5Lambda vX ', (A/F) / (A/F)3

i. 3-i1. TDE Emissions Using Natural Gas:Volumet ic Parameters 1

3-43

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S5 -

4-

TcontrolS3- *400 0C

04500Co A500C

2 Note: NOX and CO Dry SampleHC (Ref. to Methane) Wet SampleSampling Upstream of Preheater

S4-

1 2 -

1

HC

00" 2.0 2.5 3.0 3.5

Lambda ".j X e (A/F) / (A/F)3Fig. 3-17 TOE Emissions Using Natural Gas:

Mass Paraaeters 82157

3-44

.,.. .,;., a. " , , ... '. ..... . q i

e Emissions levels are extremely low. That is, NO was less thanx100 ppm and CO and HC indicate a high combustion efficiency.

0 TheTDE data compares favorably to published emissionc of theGPU-3 burning diesel fuel.

Design Data and Projected DesignBoth the EM and the ADP are being designed to achieve low ch,-mical enmmissionsfrom liquid fuel sources. Much of the appropriate technology to accomplishthis is being developed under the DOE Automotive Stirling Engine Program.

3.2,6 Fuel System Safety

Requirements

Paragraph 4.5 of MIL-STD-1472A requires that a fail-safe design be provided.in those areas where failure can disable the system or cause catastrophethrough damage to equipment, injury to personnel, or inadvertent operationof critical equipment.

Test Data

The Stirling engine combustion system, operating at essentially atmosphericpressure, is no more dangerous than a residential gas- or oil-fired furnace/boiler or vehicle internal conibuvticn engine. The potential hazards of theStirling engine or any other fossil fuel combustion system are:

* Fuel leakage, i.e., harmful vapor, explosion or fire.

e Combining the combustion process to the system designed forthat purpose.

* Leakage of combustion products containing carbon monoxide.

For "Prototype Engine" fuel system, a number of safety features are provided.Starting at the natural gas supply, a pressure switch indicates pressuresthat are either too high or too low. If either condition occurs, provisionsexist to shut the engine down. For positive control there is an on/off sole-noid switch to stop the flow of natural gas when the engine is not in use.

3-45

. . . .. , :. . . .. , o.. ... , . , .... , ,. .... .. . .... ......... .. .

..

,., ,,,

I .In order to open the solenoid, it is necessary for the test cell exhaust fanto be on, thus ensuring adequate ventilation if there should be leaks ineither the gas or engine exhaust systems. After the solenoid, there is a controlvalve to adjust heat input to the cngine. In the event of failure, the valvewill automatically close. If a loss of air supply occurs, provisions existto automatically shut off fuel. Finally, once the engine is shut down, theblower is left on to cool the hot parts and to purge the combustion systemof unburned fuel and products of combustion.

For the P-40 Automotive Stirling Engine (ASE) to burn unleaded gasoxine, anon/off fuel solenoid valve is also used. Should loss of air occur, the BoschK-Jetronic air/fuel controller will sense the loss ot air and stop fuel flow.After shutdown, the atomizing air is left on to purge the nozzle of fuel sothat it does not drop on the hot parts and ignite.

Both FPSE and ASE combustors are designed to aerodynamically stabilize the

combustion process in a predetermined volume through the use of swirling air.By suitably locating the ignitor and fuel injector and by providing a swirlinduced recirculating region, a flame is prevented from occurring upstreamof the combustor. By providing a larger than necessary combustor volume,combustion is complete before the heater head. As a further safeguard, theignitor of the P-40 engine is always on.

In summary, the potential for natural gas, liquid fuel and exhaust system

leakage or combustion external to the burner is no greater than currentresidential, commercial, military or vehicle systems burning fossil fuels.

Design Data and Projected Design

Both the EM and the ADP will be dejigned to incorporate safety controls thatwill provide for complete fail-safe operation of the liquid fuel combustor.

3-46

V .

SUBSECTION 3.3

AUDIO CO!4PARI SON

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3.3 Audio Comparison

Requirements

The purchase description requirement for noise states:

"The power source shall be inaudible to the unaided ear of anSobserver located in a quiet jungle background 100 meters from

the power source. Compliance with this requirement will be

considered to be demonstrated when the audio noise sound pres-

sure levels emanating from the set during operation from no

load to full rated load meet the following criteria when themicrophone is located 1.2 meters above the ground on a 6 meter

radius circle measured in any direction from the geometrical

center of the set.

Octave Band Center Maximum Noise Level inFrequency, Hz Decibels re/ .0002 Microbar

63 60

125 46

250 44

. 500 45

1000 452000 46

4000 47

8000 48

During acoustical measurements, the ambient background noise

levels, including wind noise, shall be at least 10 db below

that of the set noise in each octave band."

Test Data

Stirling engines are inherently quiet due to the continuous atmospheric com-

bustion means of Inputtirg energy to the working cycle. Free-piston Stirlingengines have even a greater capacity for quiet operation due to the utiliza-

tion of onlv two moving parts on gas hearings.

3-47

Noise measurements were taken of the TDE in operation in its test cell inorder to establish a frame of reference for estimating initial FPSE systemoperational noise. Figure 3-18 illustrates the test environment in which thenoise measurement was made. As illustrated, the test cell environment pro-vided for a high degree of reverberation as indicated by the dramatic differ-ence between the measurements taken with the cell door open and the cell doorclosed. The measurements were taken at one point with a B&K type 2203 noisemeter over the full frequency range. The noise sources were determined to bethe engine/alternator and combustor subsystem, as well as the experimentalmounting frame and an external gas bearing pump. No attempt was made to

simulate noise that would be generated by the coolant system exhaust fan.

Although the test set-up was admittedly crude, the test results, shown inFigure 3-18, are indicative of the potential of the FPSE to meet the militaryrequirements for silent power systems.

Design Data and Projected Design

It is probable that, in a completely packaged FPSE generator system, the majornoise source contribution would be from the coolant system radiator fan andmotor. Therefore, care was taken in the EM and ADP radiator system design tominimize the audio emission potential. The following elements were considered ~to minimize noise emissions:

e Torin radiator fans were selected so that the required airf low matched the maximum fan efficiency. This should producethe lowest sound pressure level (SPL).

a Relatively low speed (1140 rpm) was selected for a low SPL.

e The fan and pump motor mounts will be vibration-isolated

from the system frame.

9 The EM frame includes an enclosure that contains soundinsulating materials to baffle any high-frequency emissions.Figut, -19) illustrates the frame enclosure envisioned

for the EM.:1

3-48

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, "k

+- Whe CL

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3-49

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3-50

SUBSECTION 3.4

MATERIAL COMPARISON

.............. ..........

. ..........

3.4Matrials omprison

Requirements

The purchase description material guideline states

"Material used shall be of good commercial quality for thepurpose intended. Materials which are latest state-of-the-art may be considered in order to achieve design objectives.In all cases materials used should be consistent with strengthrequired for performance, safety and reliability."

Test Data

P. The materials used to construct the TDE and "Prototype Engine" are listed inTables 3-13 and Table 3-14 respectively. The materials listed are consistentwith the materials requirements.

DeinData

Table 3-15 indicates the compliance with requirements of the materials selected

for fabrication of the EM system.

Projected DesignThe ADP will incorporate commonly available engineering materials in its de-

sign as does the EM system. One item is, however, worth noting: The dramaticweight reduction that will be accomplished in the ADP alternator system re-

quires the use of 2 lb of samarium cobalt permanent magnets. The decrease in

system weight, however, will compensate for the use of the increased cost

permanent magnet material. it should be noted, however, that alternative

magnets, are being considered for their impact on system weight.A

3-51

TABLE 3-13TDE MATERIALS LIST

Combustor:'V Fuel. nozzle Brass

Recuperator 316 SSCombustor cup 316 SS or 310 SS or Inco 625Combustor liner Kaowool

B&W Kaowool (Alumina Oxide Fiber)

Engine:

Displacer 316 SSHeater head Inconel 617Regenerator 304 SS

Cooler AluminumPressure vessel 304 SS

Alternator:Stator & Plunger Hypereo 50/CopperBearings/Piston/Cylinder Chrome Oxide/Aluminum

Gas Spring Aluminum

3-52

q.\ j

TABLE 3-14PROTOTYPE ENGINE MATERIALS LIST

Combustor:Fuel nozzle assembly Brass

Recuperator 316 SS

Combustor cups 310 SS

Engine:

Displacer assembly 316 SS

Diaphragm packs 301 SS

Heater head 316 SSHeater tubes 316 SSRegenerator 304 SS

Cooler Aluminum

Alternator:Stator Iron/CopperPlunger Iron

BearInngs,/Pistons/Cylinders Cr0 2 Coated Aluminum

Gas springs Aluminum

3-53

TABLE 3-15

EM MATERIALS LIST

Combustor:Fuel Nozzle BrassRecuperator 316-SS

Combustor Cup 316-SS or 310-SS or Inco-625Combustor Liner Kaowool

B&W Kaowool (Aluminum Oxide Fiber)

Engine:

I# "'Displacer 316-SS

Heater Head Inconel, 718Regenerator 304-SSCooler AluminumPressure Vessel Low Alloy Steel

Alternator:

Stator & Plunger Hyperco-50/CopperBearings/Piston/Cylinder Chrome Oxide/Aluminum

3-54

SUBSECTION 3.5

OPERATIONAL PARAMETERS

"I~

.LI

3.5 Operational Parameters

Operational parameters are considered as those items that characterize systemoperation. Table 3-16 summarizes the comparison of operational parameterswith military requirements. As indicated, the FPSE is expected to meet orexceed each of the requirements.

3.5.1 Power

Reurement

The purchase description requires the generator set to be capable of producingcontinuous power of 3 kW.

Test Data

The TDE was designed for 1 kW electrical power output at 720 *C. Althoughmechanical constraints presently preclude operation at the maximum tempera-ture point, the design power output level was exceeded. Figure 3-20 illus-trates the thermodynamic power output that was achieved by the TDE as afunction of heater head temperature.

Design Data

The EM is designed to have a gross electric power output of 3800 W. The para-sitic load required to operate the auxiliaries and the control system, however,will require 480 W and the new available power output will be 3.3 MW

Pro-jected Design

The EM is designed to have a certain degree of design margin to ensure thatat least 3 kW electric is available to the user. Based on performance testingof the EM, the ADP will be scaled accordingly to provide precisely 3 kW ratedpower output.

3.5.2 Frequency

RequirementsIMIL-STD-1332B requires that the generator maintain an operating frequency of60 Hz.

3-55

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00

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00.

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2000Pm = 40 barf = 45 Hz

Stroke = 2.2 cm1800

li.

1600A

S1400iS

iIt

1200

J" " 10001

800

600- I ,200 300 400 500 600

Mean Heat'lr Head Temperature (0C)411596

Fig. 3-20 TDE Thermodynamic Power Output

3-57)..

Test Data

FPSEs perform as thermal oscillators and operate at the resonant frequency as

determined by the system dynamic design parameters (charge pressure, area, andpiston mass). The TDE has been operated up to its resonant frequency of 45 Hz.

The "Prototype Engine" was designed to operate a~t higher frequency levels"e ~and, in fact, achieved regular operation at 60 Hz.

Design Data and Design Projection

The EM has been designed to operate at 60 Hz. The ADP will also be designedto operate at 60 Hz.

3.5.3 Climatic Conditions

Requirements

The purchase description states:

"The engine shall be capable of starting and carrying rated load

within 10 minutes in any ambient temperature between minus 25*F4 and plus 125*F without external starting aids. From minus 25*F

to minus 50*F, external heat may be applied for starting and theengine shall be capable of carrying load within 30 minutes."

Test Data

The method for starting the TDE is to apply heat to the heater head whilemotoring the al~ternator piston until positive power output is developed.This technique has worked well with cold starts (heater head at ambient temn-perature) ant' with warm starts (heater head at elevated temperature).

Design Data

There are two issues involved here: ability to maintain rated load and start-up time for a range of ambient temperatures. These two issues are addressedin the following discussion.

3-58

1' . .Design calculations were performed for the EM to determine the change inperformance expected between operation at the design point condition of 90*Fand operation at an ambient temperature of -25*F. The calculations wereperformed assuming two separate methods of combustor control:

Case 1: Variable speed air blower with fixed fuel/air mass control

Case 2: Variable speed air blower with fixed fuel/air (F/A) volumecontrol.

The 90*F da